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1<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
2"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
3[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
4
5<chapter id='dev-manual-newbie'>
6
7<title>The Yocto Project Open Source Development Environment</title>
8
9<para>
10 This chapter helps you understand the Yocto Project as an open source development project.
11 In general, working in an open source environment is very different from working in a
12 closed, proprietary environment.
13 Additionally, the Yocto Project uses specific tools and constructs as part of its development
14 environment.
15 This chapter specifically addresses open source philosophy, using the
16 Yocto Project in a team environment, source repositories, Yocto Project
17 terms, licensing, the open source distributed version control system Git,
18 workflows, bug tracking, and how to submit changes.
19</para>
20
21<section id='open-source-philosophy'>
22 <title>Open Source Philosophy</title>
23
24 <para>
25 Open source philosophy is characterized by software development directed by peer production
26 and collaboration through an active community of developers.
27 Contrast this to the more standard centralized development models used by commercial software
28 companies where a finite set of developers produces a product for sale using a defined set
29 of procedures that ultimately result in an end product whose architecture and source material
30 are closed to the public.
31 </para>
32
33 <para>
34 Open source projects conceptually have differing concurrent agendas, approaches, and production.
35 These facets of the development process can come from anyone in the public (community) that has a
36 stake in the software project.
37 The open source environment contains new copyright, licensing, domain, and consumer issues
38 that differ from the more traditional development environment.
39 In an open source environment, the end product, source material, and documentation are
40 all available to the public at no cost.
41 </para>
42
43 <para>
44 A benchmark example of an open source project is the Linux Kernel, which was initially conceived
45 and created by Finnish computer science student Linus Torvalds in 1991.
46 Conversely, a good example of a non-open source project is the
47 <trademark class='registered'>Windows</trademark> family of operating
48 systems developed by <trademark class='registered'>Microsoft</trademark> Corporation.
49 </para>
50
51 <para>
52 Wikipedia has a good historical description of the Open Source Philosophy
53 <ulink url='http://en.wikipedia.org/wiki/Open_source'>here</ulink>.
54 You can also find helpful information on how to participate in the Linux Community
55 <ulink url='http://ldn.linuxfoundation.org/book/how-participate-linux-community'>here</ulink>.
56 </para>
57</section>
58
59<section id="usingpoky-changes-collaborate">
60 <title>Using the Yocto Project in a Team Environment</title>
61
62 <para>
63 It might not be immediately clear how you can use the Yocto
64 Project in a team environment, or scale it for a large team of
65 developers.
66 One of the strengths of the Yocto Project is that it is extremely
67 flexible.
68 Thus, you can adapt it to many different use cases and scenarios.
69 However, these characteristics can cause a struggle if you are trying
70 to create a working setup that scales across a large team.
71 </para>
72
73 <para>
74 To help with these types of situations, this section presents
75 some of the project's most successful experiences,
76 practices, solutions, and available technologies that work well.
77 Keep in mind, the information here is a starting point.
78 You can build off it and customize it to fit any
79 particular working environment and set of practices.
80 </para>
81
82 <section id='best-practices-system-configurations'>
83 <title>System Configurations</title>
84
85 <para>
86 Systems across a large team should meet the needs of
87 two types of developers: those working on the contents of the
88 operating system image itself and those developing applications.
89 Regardless of the type of developer, their workstations must
90 be both reasonably powerful and run Linux.
91 </para>
92
93 <section id='best-practices-application-development'>
94 <title>Application Development</title>
95
96 <para>
97 For developers who mainly do application level work
98 on top of an existing software stack,
99 here are some practices that work best:
100 <itemizedlist>
101 <listitem><para>Use a pre-built toolchain that
102 contains the software stack itself.
103 Then, develop the application code on top of the
104 stack.
105 This method works well for small numbers of relatively
106 isolated applications.</para></listitem>
107 <listitem><para>When possible, use the Yocto Project
108 plug-in for the <trademark class='trade'>Eclipse</trademark> IDE
109 and other pieces of Application Development
110 Technology (ADT).
111 For more information, see the
112 "<link linkend='application-development-workflow'>Application
113 Development Workflow</link>" section as well as the
114 <ulink url='&YOCTO_DOCS_ADT_URL;'>Yocto Project Application Developer's Guide</ulink>.
115 </para></listitem>
116 <listitem><para>Keep your cross-development toolchains
117 updated.
118 You can do this through provisioning either as new
119 toolchain downloads or as updates through a package
120 update mechanism using <filename>opkg</filename>
121 to provide updates to an existing toolchain.
122 The exact mechanics of how and when to do this are a
123 question for local policy.</para></listitem>
124 <listitem><para>Use multiple toolchains installed locally
125 into different locations to allow development across
126 versions.</para></listitem>
127 </itemizedlist>
128 </para>
129 </section>
130
131 <section id='best-practices-core-system-development'>
132 <title>Core System Development</title>
133
134 <para>
135 For core system development, it is often best to have the
136 build system itself available on the developer workstations
137 so developers can run their own builds and directly
138 rebuild the software stack.
139 You should keep the core system unchanged as much as
140 possible and do your work in layers on top of the core system.
141 Doing so gives you a greater level of portability when
142 upgrading to new versions of the core system or Board
143 Support Packages (BSPs).
144 You can share layers amongst the developers of a particular
145 project and contain the policy configuration that defines
146 the project.
147 </para>
148
149 <para>
150 Aside from the previous best practices, there exists a number
151 of tips and tricks that can help speed up core development
152 projects:
153 <itemizedlist>
154 <listitem><para>Use a
155 <ulink url='&YOCTO_DOCS_REF_URL;#shared-state-cache'>Shared State Cache</ulink>
156 (sstate) among groups of developers who are on a
157 fast network.
158 The best way to share sstate is through a
159 Network File System (NFS) share.
160 The first user to build a given component for the
161 first time contributes that object to the sstate,
162 while subsequent builds from other developers then
163 reuse the object rather than rebuild it themselves.
164 </para>
165 <para>Although it is possible to use other protocols for the
166 sstate such as HTTP and FTP, you should avoid these.
167 Using HTTP limits the sstate to read-only and
168 FTP provides poor performance.
169 </para></listitem>
170 <listitem><para>Have autobuilders contribute to the sstate
171 pool similarly to how the developer workstations
172 contribute.
173 For information, see the
174 "<link linkend='best-practices-autobuilders'>Autobuilders</link>"
175 section.</para></listitem>
176 <listitem><para>Build stand-alone tarballs that contain
177 "missing" system requirements if for some reason
178 developer workstations do not meet minimum system
179 requirements such as latest Python versions,
180 <filename>chrpath</filename>, or other tools.
181 You can install and relocate the tarball exactly as you
182 would the usual cross-development toolchain so that
183 all developers can meet minimum version requirements
184 on most distributions.</para></listitem>
185 <listitem><para>Use a small number of shared,
186 high performance systems for testing purposes
187 (e.g. dual, six-core Xeons with 24 Gbytes of RAM
188 and plenty of disk space).
189 Developers can use these systems for wider, more
190 extensive testing while they continue to develop
191 locally using their primary development system.
192 </para></listitem>
193 <listitem><para>Enable the PR Service when package feeds
194 need to be incremental with continually increasing
195 <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'>PR</ulink>
196 values.
197 Typically, this situation occurs when you use or
198 publish package feeds and use a shared state.
199 You should enable the PR Service for all users who
200 use the shared state pool.
201 For more information on the PR Service, see the
202 "<link linkend='working-with-a-pr-service'>Working With a PR Service</link>".
203 </para></listitem>
204 </itemizedlist>
205 </para>
206 </section>
207 </section>
208
209 <section id='best-practices-source-control-management'>
210 <title>Source Control Management (SCM)</title>
211
212 <para>
213 Keeping your
214 <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>
215 and any software you are developing under the
216 control of an SCM system that is compatible
217 with the OpenEmbedded build system is advisable.
218 Of the SCMs BitBake supports, the
219 Yocto Project team strongly recommends using
220 <link linkend='git'>Git</link>.
221 Git is a distributed system that is easy to backup,
222 allows you to work remotely, and then connects back to the
223 infrastructure.
224 <note>
225 For information about BitBake, see the
226 <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
227 </note>
228 </para>
229
230 <para>
231 It is relatively easy to set up Git services and create
232 infrastructure like
233 <ulink url='&YOCTO_GIT_URL;'>http://git.yoctoproject.org</ulink>,
234 which is based on server software called
235 <filename>gitolite</filename> with <filename>cgit</filename>
236 being used to generate the web interface that lets you view the
237 repositories.
238 The <filename>gitolite</filename> software identifies users
239 using SSH keys and allows branch-based
240 access controls to repositories that you can control as little
241 or as much as necessary.
242 </para>
243
244 <note>
245 The setup of these services is beyond the scope of this manual.
246 However, sites such as these exist that describe how to perform
247 setup:
248 <itemizedlist>
249 <listitem><para><ulink url='http://git-scm.com/book/ch4-8.html'>Git documentation</ulink>:
250 Describes how to install <filename>gitolite</filename>
251 on the server.</para></listitem>
252 <listitem><para><ulink url='http://sitaramc.github.com/gitolite/master-toc.html'>The <filename>gitolite</filename> master index</ulink>:
253 All topics for <filename>gitolite</filename>.
254 </para></listitem>
255 <listitem><para><ulink url='https://git.wiki.kernel.org/index.php/Interfaces,_frontends,_and_tools'>Interfaces, frontends, and tools</ulink>:
256 Documentation on how to create interfaces and frontends
257 for Git.</para></listitem>
258 </itemizedlist>
259 </note>
260 </section>
261
262 <section id='best-practices-autobuilders'>
263 <title>Autobuilders</title>
264
265 <para>
266 Autobuilders are often the core of a development project.
267 It is here that changes from individual developers are brought
268 together and centrally tested and subsequent decisions about
269 releases can be made.
270 Autobuilders also allow for "continuous integration" style
271 testing of software components and regression identification
272 and tracking.
273 </para>
274
275 <para>
276 See "<ulink url='http://autobuilder.yoctoproject.org'>Yocto Project Autobuilder</ulink>"
277 for more information and links to buildbot.
278 The Yocto Project team has found this implementation
279 works well in this role.
280 A public example of this is the Yocto Project
281 Autobuilders, which we use to test the overall health of the
282 project.
283 </para>
284
285 <para>
286 The features of this system are:
287 <itemizedlist>
288 <listitem><para>Highlights when commits break the build.
289 </para></listitem>
290 <listitem><para>Populates an sstate cache from which
291 developers can pull rather than requiring local
292 builds.</para></listitem>
293 <listitem><para>Allows commit hook triggers,
294 which trigger builds when commits are made.
295 </para></listitem>
296 <listitem><para>Allows triggering of automated image booting
297 and testing under the QuickEMUlator (QEMU).
298 </para></listitem>
299 <listitem><para>Supports incremental build testing and
300 from-scratch builds.</para></listitem>
301 <listitem><para>Shares output that allows developer
302 testing and historical regression investigation.
303 </para></listitem>
304 <listitem><para>Creates output that can be used for releases.
305 </para></listitem>
306 <listitem><para>Allows scheduling of builds so that resources
307 can be used efficiently.</para></listitem>
308 </itemizedlist>
309 </para>
310 </section>
311
312 <section id='best-practices-policies-and-change-flow'>
313 <title>Policies and Change Flow</title>
314
315 <para>
316 The Yocto Project itself uses a hierarchical structure and a
317 pull model.
318 Scripts exist to create and send pull requests
319 (i.e. <filename>create-pull-request</filename> and
320 <filename>send-pull-request</filename>).
321 This model is in line with other open source projects where
322 maintainers are responsible for specific areas of the project
323 and a single maintainer handles the final "top-of-tree" merges.
324 </para>
325
326 <note>
327 You can also use a more collective push model.
328 The <filename>gitolite</filename> software supports both the
329 push and pull models quite easily.
330 </note>
331
332 <para>
333 As with any development environment, it is important
334 to document the policy used as well as any main project
335 guidelines so they are understood by everyone.
336 It is also a good idea to have well structured
337 commit messages, which are usually a part of a project's
338 guidelines.
339 Good commit messages are essential when looking back in time and
340 trying to understand why changes were made.
341 </para>
342
343 <para>
344 If you discover that changes are needed to the core layer of the
345 project, it is worth sharing those with the community as soon
346 as possible.
347 Chances are if you have discovered the need for changes, someone
348 else in the community needs them also.
349 </para>
350 </section>
351
352 <section id='best-practices-summary'>
353 <title>Summary</title>
354
355 <para>
356 This section summarizes the key recommendations described in the
357 previous sections:
358 <itemizedlist>
359 <listitem><para>Use <link linkend='git'>Git</link>
360 as the source control system.</para></listitem>
361 <listitem><para>Maintain your Metadata in layers that make sense
362 for your situation.
363 See the "<link linkend='understanding-and-creating-layers'>Understanding
364 and Creating Layers</link>" section for more information on
365 layers.</para></listitem>
366 <listitem><para>
367 Separate the project's Metadata and code by using
368 separate Git repositories.
369 See the
370 "<link linkend='yocto-project-repositories'>Yocto Project Source Repositories</link>"
371 section for information on these repositories.
372 See the
373 "<link linkend='getting-setup'>Getting Set Up</link>"
374 section for information on how to set up local Git
375 repositories for related upstream Yocto Project
376 Git repositories.
377 </para></listitem>
378 <listitem><para>Set up the directory for the shared state cache
379 (<ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>)
380 where it makes sense.
381 For example, set up the sstate cache on a system used
382 by developers in the same organization and share the
383 same source directories on their machines.
384 </para></listitem>
385 <listitem><para>Set up an Autobuilder and have it populate the
386 sstate cache and source directories.</para></listitem>
387 <listitem><para>The Yocto Project community encourages you
388 to send patches to the project to fix bugs or add features.
389 If you do submit patches, follow the project commit
390 guidelines for writing good commit messages.
391 See the "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
392 section.</para></listitem>
393 <listitem><para>Send changes to the core sooner than later
394 as others are likely to run into the same issues.
395 For some guidance on mailing lists to use, see the list in the
396 "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
397 section.
398 For a description of the available mailing lists, see the
399 "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing Lists</ulink>"
400 section in the Yocto Project Reference Manual.
401 </para></listitem>
402 </itemizedlist>
403 </para>
404 </section>
405</section>
406
407<section id='yocto-project-repositories'>
408 <title>Yocto Project Source Repositories</title>
409
410 <para>
411 The Yocto Project team maintains complete source repositories for all
412 Yocto Project files at
413 <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'></ulink>.
414 This web-based source code browser is organized into categories by
415 function such as IDE Plugins, Matchbox, Poky, Yocto Linux Kernel, and
416 so forth.
417 From the interface, you can click on any particular item in the "Name"
418 column and see the URL at the bottom of the page that you need to clone
419 a Git repository for that particular item.
420 Having a local Git repository of the
421 <link linkend='source-directory'>Source Directory</link>, which is
422 usually named "poky", allows
423 you to make changes, contribute to the history, and ultimately enhance
424 the Yocto Project's tools, Board Support Packages, and so forth.
425 </para>
426
427 <para>
428 For any supported release of Yocto Project, you can also go to the
429 <ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink> and
430 select the "Downloads" tab and get a released tarball of the
431 <filename>poky</filename> repository or any supported BSP tarballs.
432 Unpacking these tarballs gives you a snapshot of the released
433 files.
434 <note><title>Notes</title>
435 <itemizedlist>
436 <listitem><para>
437 The recommended method for setting up the Yocto Project
438 <link linkend='source-directory'>Source Directory</link>
439 and the files for supported BSPs
440 (e.g., <filename>meta-intel</filename>) is to use
441 <link linkend='git'>Git</link> to create a local copy of
442 the upstream repositories.
443 </para></listitem>
444 <listitem><para>
445 Be sure to always work in matching branches for both
446 the <filename>meta-intel</filename> repository and the
447 <link linkend='source-directory'>Source Directory</link>
448 (i.e. <filename>poky</filename>) repository.
449 For example, if you have checked out the "master" branch
450 of <filename>poky</filename> and you are going to use
451 <filename>meta-intel</filename>, be sure to checkout the
452 "master" branch of <filename>meta-intel</filename>.
453 </para></listitem>
454 </itemizedlist>
455 </note>
456 </para>
457
458 <para>
459 In summary, here is where you can get the project files needed for development:
460 <itemizedlist>
461 <listitem><para id='source-repositories'><emphasis><ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'>Source Repositories:</ulink></emphasis>
462 This area contains IDE Plugins, Matchbox, Poky, Poky Support, Tools, Yocto Linux Kernel, and Yocto
463 Metadata Layers.
464 You can create local copies of Git repositories for each of these areas.</para>
465 <para>
466 <imagedata fileref="figures/source-repos.png" align="center" width="6in" depth="4in" />
467 </para></listitem>
468 <listitem><para><anchor id='index-downloads' /><emphasis><ulink url='&YOCTO_DL_URL;/releases/'>Index of /releases:</ulink></emphasis>
469 This is an index of releases such as
470 the <trademark class='trade'>Eclipse</trademark>
471 Yocto Plug-in, miscellaneous support, Poky, Pseudo, installers for cross-development toolchains,
472 and all released versions of Yocto Project in the form of images or tarballs.
473 Downloading and extracting these files does not produce a local copy of the
474 Git repository but rather a snapshot of a particular release or image.</para>
475 <para>
476 <imagedata fileref="figures/index-downloads.png" align="center" width="6in" depth="3.5in" />
477 </para></listitem>
478 <listitem><para><emphasis>"Downloads" page for the
479 <ulink url='&YOCTO_HOME_URL;'>Yocto Project Website</ulink>:</emphasis>
480 Access this page by going to the website and then selecting
481 the "Downloads" tab.
482 This page allows you to download any Yocto Project
483 release or Board Support Package (BSP) in tarball form.
484 The tarballs are similar to those found in the
485 <ulink url='&YOCTO_DL_URL;/releases/'>Index of /releases:</ulink> area.</para>
486 <para>
487 <imagedata fileref="figures/yp-download.png" align="center" width="6in" depth="4in" />
488 </para></listitem>
489 </itemizedlist>
490 </para>
491</section>
492
493<section id='yocto-project-terms'>
494 <title>Yocto Project Terms</title>
495
496 <para>
497 Following is a list of terms and definitions users new to the Yocto Project development
498 environment might find helpful.
499 While some of these terms are universal, the list includes them just in case:
500 <itemizedlist>
501 <listitem><para><emphasis>Append Files:</emphasis> Files that append build information to
502 a recipe file.
503 Append files are known as BitBake append files and <filename>.bbappend</filename> files.
504 The OpenEmbedded build system expects every append file to have a corresponding
505 recipe (<filename>.bb</filename>) file.
506 Furthermore, the append file and corresponding recipe file
507 must use the same root filename.
508 The filenames can differ only in the file type suffix used (e.g.
509 <filename>formfactor_0.0.bb</filename> and <filename>formfactor_0.0.bbappend</filename>).
510 </para>
511 <para>Information in append files overrides the information in the similarly-named recipe file.
512 For an example of an append file in use, see the
513 "<link linkend='using-bbappend-files'>Using .bbappend Files</link>" section.
514 </para></listitem>
515 <listitem><para id='bitbake-term'><emphasis>BitBake:</emphasis>
516 The task executor and scheduler used by the OpenEmbedded build
517 system to build images.
518 For more information on BitBake, see the
519 <ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
520 </para></listitem>
521 <listitem>
522 <para id='build-directory'><emphasis>Build Directory:</emphasis>
523 This term refers to the area used by the OpenEmbedded build
524 system for builds.
525 The area is created when you <filename>source</filename> the
526 setup environment script that is found in the Source Directory
527 (i.e. <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
528 or
529 <ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>).
530 The <ulink url='&YOCTO_DOCS_REF_URL;#var-TOPDIR'><filename>TOPDIR</filename></ulink>
531 variable points to the Build Directory.</para>
532
533 <para>
534 You have a lot of flexibility when creating the Build
535 Directory.
536 Following are some examples that show how to create the
537 directory.
538 The examples assume your
539 <link linkend='source-directory'>Source Directory</link> is
540 named <filename>poky</filename>:
541 <itemizedlist>
542 <listitem><para>Create the Build Directory inside your
543 Source Directory and let the name of the Build
544 Directory default to <filename>build</filename>:
545 <literallayout class='monospaced'>
546 $ cd $HOME/poky
547 $ source &OE_INIT_FILE;
548 </literallayout></para></listitem>
549 <listitem><para>Create the Build Directory inside your
550 home directory and specifically name it
551 <filename>test-builds</filename>:
552 <literallayout class='monospaced'>
553 $ cd $HOME
554 $ source poky/&OE_INIT_FILE; test-builds
555 </literallayout></para></listitem>
556 <listitem><para>
557 Provide a directory path and
558 specifically name the Build Directory.
559 Any intermediate folders in the pathname must
560 exist.
561 This next example creates a Build Directory named
562 <filename>YP-&POKYVERSION;</filename>
563 in your home directory within the existing
564 directory <filename>mybuilds</filename>:
565 <literallayout class='monospaced'>
566 $cd $HOME
567 $ source $HOME/poky/&OE_INIT_FILE; $HOME/mybuilds/YP-&POKYVERSION;
568 </literallayout></para></listitem>
569 </itemizedlist>
570 <note>
571 By default, the Build Directory contains
572 <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>,
573 which is a temporary directory the build system uses for
574 its work.
575 <filename>TMPDIR</filename> cannot be under NFS.
576 Thus, by default, the Build Directory cannot be under NFS.
577 However, if you need the Build Directory to be under NFS,
578 you can set this up by setting <filename>TMPDIR</filename>
579 in your <filename>local.conf</filename> file
580 to use a local drive.
581 Doing so effectively separates <filename>TMPDIR</filename>
582 from <filename>TOPDIR</filename>, which is the Build
583 Directory.
584 </note>
585 </para></listitem>
586 <listitem><para id='build-system-term'><emphasis>Build System:</emphasis>
587 In the context of the Yocto Project,
588 this term refers to the OpenEmbedded build system used by the project.
589 This build system is based on the project known as "Poky."
590 For some historical information about Poky, see the
591 <link linkend='poky'>Poky</link> term.
592 </para></listitem>
593 <listitem><para><emphasis>Classes:</emphasis> Files that provide for logic encapsulation
594 and inheritance so that commonly used patterns can be defined once and then easily used
595 in multiple recipes.
596 For reference information on the Yocto Project classes, see the
597 "<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes'>Classes</ulink>" chapter of the
598 Yocto Project Reference Manual.
599 Class files end with the <filename>.bbclass</filename> filename extension.
600 </para></listitem>
601 <listitem><para><emphasis>Configuration File:</emphasis>
602 Configuration information in various <filename>.conf</filename>
603 files provides global definitions of variables.
604 The <filename>conf/local.conf</filename> configuration file in
605 the
606 <link linkend='build-directory'>Build Directory</link>
607 contains user-defined variables that affect every build.
608 The <filename>meta-yocto/conf/distro/poky.conf</filename>
609 configuration file defines Yocto "distro" configuration
610 variables used only when building with this policy.
611 Machine configuration files, which
612 are located throughout the
613 <link linkend='source-directory'>Source Directory</link>, define
614 variables for specific hardware and are only used when building
615 for that target (e.g. the
616 <filename>machine/beaglebone.conf</filename> configuration
617 file defines variables for the Texas Instruments ARM Cortex-A8
618 development board).
619 Configuration files end with a <filename>.conf</filename>
620 filename extension.
621 </para></listitem>
622 <listitem><para id='cross-development-toolchain'>
623 <emphasis>Cross-Development Toolchain:</emphasis>
624 In general, a cross-development toolchain is a collection of
625 software development tools and utilities that run on one
626 architecture and allow you to develop software for a
627 different, or targeted, architecture.
628 These toolchains contain cross-compilers, linkers, and
629 debuggers that are specific to the target architecture.
630 </para>
631
632 <para>The Yocto Project supports two different cross-development
633 toolchains:
634 <itemizedlist>
635 <listitem><para>A toolchain only used by and within
636 BitBake when building an image for a target
637 architecture.</para></listitem>
638 <listitem><para>A relocatable toolchain used outside of
639 BitBake by developers when developing applications
640 that will run on a targeted device.
641 Sometimes this relocatable cross-development
642 toolchain is referred to as the meta-toolchain.
643 </para></listitem>
644 </itemizedlist>
645 </para>
646
647 <para>
648 Creation of these toolchains is simple and automated.
649 For information on toolchain concepts as they apply to the
650 Yocto Project, see the
651 "<ulink url='&YOCTO_DOCS_REF_URL;#cross-development-toolchain-generation'>Cross-Development Toolchain Generation</ulink>"
652 section in the Yocto Project Reference Manual.
653 You can also find more information on using the
654 relocatable toolchain in the
655 <ulink url='&YOCTO_DOCS_ADT_URL;'>Yocto Project
656 Application Developer's Guide</ulink>.
657 </para></listitem>
658 <listitem><para><emphasis>Image:</emphasis>
659 An image is the result produced when BitBake processes a given
660 collection of recipes and related Metadata.
661 Images are the binary output that run on specific hardware or
662 QEMU and are used for specific use-cases.
663 For a list of the supported image types that the Yocto Project provides, see the
664 "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
665 chapter in the Yocto Project Reference Manual.</para></listitem>
666 <listitem><para id='layer'><emphasis>Layer:</emphasis> A collection of recipes representing the core,
667 a BSP, or an application stack.
668 For a discussion on BSP Layers, see the
669 "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
670 section in the Yocto Project Board Support Packages (BSP)
671 Developer's Guide.</para></listitem>
672 <listitem><para id='meta-toolchain'><emphasis>Meta-Toolchain:</emphasis>
673 A term sometimes used for
674 <link linkend='cross-development-toolchain'>Cross-Development Toolchain</link>.
675 </para></listitem>
676 <listitem><para id='metadata'><emphasis>Metadata:</emphasis>
677 The files that BitBake parses when building an image.
678 In general, Metadata includes recipes, classes, and
679 configuration files.
680 In the context of the kernel ("kernel Metadata"),
681 it refers to Metadata in the <filename>meta</filename>
682 branches of the kernel source Git repositories.
683 </para></listitem>
684 <listitem><para id='oe-core'><emphasis>OE-Core:</emphasis> A core set of Metadata originating
685 with OpenEmbedded (OE) that is shared between OE and the Yocto Project.
686 This Metadata is found in the <filename>meta</filename> directory of the
687 <link linkend='source-directory'>Source Directory</link>.</para></listitem>
688 <listitem><para><emphasis>Package:</emphasis>
689 In the context of the Yocto Project, this term refers a
690 recipe's packaged output produced by BitBake (i.e. a
691 "baked recipe").
692 A package is generally the compiled binaries produced from the
693 recipe's sources.
694 You "bake" something by running it through BitBake.</para>
695 <para>It is worth noting that the term "package" can, in general, have subtle
696 meanings. For example, the packages referred to in the
697 "<ulink url='&YOCTO_DOCS_QS_URL;#packages'>The Packages</ulink>" section are
698 compiled binaries that when installed add functionality to your Linux
699 distribution.</para>
700 <para>Another point worth noting is that historically within the Yocto Project,
701 recipes were referred to as packages - thus, the existence of several BitBake
702 variables that are seemingly mis-named,
703 (e.g. <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>,
704 <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>, and
705 <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>).
706 </para></listitem>
707 <listitem><para><emphasis>Package Groups:</emphasis>
708 Arbitrary groups of software Recipes.
709 You use package groups to hold recipes that, when built,
710 usually accomplish a single task.
711 For example, a package group could contain the recipes for a
712 company’s proprietary or value-add software.
713 Or, the package group could contain the recipes that enable
714 graphics.
715 A package group is really just another recipe.
716 Because package group files are recipes, they end with the
717 <filename>.bb</filename> filename extension.</para></listitem>
718 <listitem><para id='poky'><emphasis>Poky:</emphasis> The term "poky" can mean several things.
719 In its most general sense, it is an open-source project that was initially developed
720 by OpenedHand. With OpenedHand, poky was developed off of the existing OpenEmbedded
721 build system becoming a build system for embedded images.
722 After Intel Corporation acquired OpenedHand, the project poky became the basis for
723 the Yocto Project's build system.</para>
724 <para>
725 Within the Yocto Project source repositories, <filename>poky</filename>
726 exists as a separate Git repository
727 that can be cloned to yield a local copy on the host system.
728 Thus, "poky" can refer to the local copy of the Source Directory used to develop within
729 the Yocto Project.</para></listitem>
730 <listitem><para><emphasis>Recipe:</emphasis>
731 A set of instructions for building packages.
732 A recipe describes where you get source code and which patches
733 to apply.
734 Recipes describe dependencies for libraries or for other
735 recipes, and they also contain configuration and compilation
736 options.
737 Recipes contain the logical unit of execution, the software
738 to build, the images to build, and use the
739 <filename>.bb</filename> file extension.
740 </para></listitem>
741 <listitem>
742 <para id='source-directory'><emphasis>Source Directory:</emphasis>
743 This term refers to the directory structure created as a result
744 of creating a local copy of the <filename>poky</filename> Git
745 repository <filename>git://git.yoctoproject.org/poky</filename>
746 or expanding a released <filename>poky</filename> tarball.
747 <note>
748 Creating a local copy of the <filename>poky</filename>
749 Git repository is the recommended method for setting up
750 your Source Directory.
751 </note>
752 Sometimes you might hear the term "poky directory" used to refer
753 to this directory structure.
754 <note>
755 The OpenEmbedded build system does not support file or
756 directory names that contain spaces.
757 Be sure that the Source Directory you use does not contain
758 these types of names.
759 </note></para>
760
761 <para>The Source Directory contains BitBake, Documentation,
762 Metadata and other files that all support the Yocto Project.
763 Consequently, you must have the Source Directory in place on
764 your development system in order to do any development using
765 the Yocto Project.</para>
766
767 <para>When you create a local copy of the Git repository, you
768 can name the repository anything you like.
769 Throughout much of the documentation, "poky"
770 is used as the name of the top-level folder of the local copy of
771 the poky Git repository.
772 So, for example, cloning the <filename>poky</filename> Git
773 repository results in a local Git repository whose top-level
774 folder is also named "poky".</para>
775
776 <para>While it is not recommended that you use tarball expansion
777 to setup the Source Directory, if you do, the top-level
778 directory name of the Source Directory is derived from the
779 Yocto Project release tarball.
780 For example, downloading and unpacking
781 <filename>&YOCTO_POKY_TARBALL;</filename> results in a
782 Source Directory whose root folder is named
783 <filename>&YOCTO_POKY;</filename>.</para>
784
785 <para>It is important to understand the differences between the
786 Source Directory created by unpacking a released tarball as
787 compared to cloning
788 <filename>git://git.yoctoproject.org/poky</filename>.
789 When you unpack a tarball, you have an exact copy of the files
790 based on the time of release - a fixed release point.
791 Any changes you make to your local files in the Source Directory
792 are on top of the release and will remain local only.
793 On the other hand, when you clone the <filename>poky</filename>
794 Git repository, you have an active development repository with
795 access to the upstream repository's branches and tags.
796 In this case, any local changes you make to the local
797 Source Directory can be later applied to active development
798 branches of the upstream <filename>poky</filename> Git
799 repository.</para>
800
801 <para>For more information on concepts related to Git
802 repositories, branches, and tags, see the
803 "<link linkend='repositories-tags-and-branches'>Repositories, Tags, and Branches</link>"
804 section.</para></listitem>
805 <listitem><para><emphasis>Task:</emphasis>
806 A unit of execution for BitBake (e.g.
807 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>,
808 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>,
809 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>,
810 and so forth).
811 </para></listitem>
812 <listitem><para><emphasis>Upstream:</emphasis> A reference to source code or repositories
813 that are not local to the development system but located in a master area that is controlled
814 by the maintainer of the source code.
815 For example, in order for a developer to work on a particular piece of code, they need to
816 first get a copy of it from an "upstream" source.</para></listitem>
817 </itemizedlist>
818 </para>
819</section>
820
821<section id='licensing'>
822 <title>Licensing</title>
823
824 <para>
825 Because open source projects are open to the public, they have different licensing structures in place.
826 License evolution for both Open Source and Free Software has an interesting history.
827 If you are interested in this history, you can find basic information here:
828 <itemizedlist>
829 <listitem><para><ulink url='http://en.wikipedia.org/wiki/Open-source_license'>Open source license history</ulink>
830 </para></listitem>
831 <listitem><para><ulink url='http://en.wikipedia.org/wiki/Free_software_license'>Free software license
832 history</ulink></para></listitem>
833 </itemizedlist>
834 </para>
835
836 <para>
837 In general, the Yocto Project is broadly licensed under the Massachusetts Institute of Technology
838 (MIT) License.
839 MIT licensing permits the reuse of software within proprietary software as long as the
840 license is distributed with that software.
841 MIT is also compatible with the GNU General Public License (GPL).
842 Patches to the Yocto Project follow the upstream licensing scheme.
843 You can find information on the MIT license at
844 <ulink url='http://www.opensource.org/licenses/mit-license.php'>here</ulink>.
845 You can find information on the GNU GPL <ulink url='http://www.opensource.org/licenses/LGPL-3.0'>
846 here</ulink>.
847 </para>
848
849 <para>
850 When you build an image using the Yocto Project, the build process uses a
851 known list of licenses to ensure compliance.
852 You can find this list in the
853 <link linkend='source-directory'>Source Directory</link> at
854 <filename>meta/files/common-licenses</filename>.
855 Once the build completes, the list of all licenses found and used during that build are
856 kept in the
857 <link linkend='build-directory'>Build Directory</link> at
858 <filename>tmp/deploy/licenses</filename>.
859 </para>
860
861 <para>
862 If a module requires a license that is not in the base list, the build process
863 generates a warning during the build.
864 These tools make it easier for a developer to be certain of the licenses with which
865 their shipped products must comply.
866 However, even with these tools it is still up to the developer to resolve potential licensing issues.
867 </para>
868
869 <para>
870 The base list of licenses used by the build process is a combination of the Software Package
871 Data Exchange (SPDX) list and the Open Source Initiative (OSI) projects.
872 <ulink url='http://spdx.org'>SPDX Group</ulink> is a working group of the Linux Foundation
873 that maintains a specification
874 for a standard format for communicating the components, licenses, and copyrights
875 associated with a software package.
876 <ulink url='http://opensource.org'>OSI</ulink> is a corporation dedicated to the Open Source
877 Definition and the effort for reviewing and approving licenses that
878 conform to the Open Source Definition (OSD).
879 </para>
880
881 <para>
882 You can find a list of the combined SPDX and OSI licenses that the
883 Yocto Project uses in the
884 <filename>meta/files/common-licenses</filename> directory in your
885 <link linkend='source-directory'>Source Directory</link>.
886 </para>
887
888 <para>
889 For information that can help you maintain compliance with various
890 open source licensing during the lifecycle of a product created using
891 the Yocto Project, see the
892 "<link linkend='maintaining-open-source-license-compliance-during-your-products-lifecycle'>Maintaining Open Source License Compliance During Your Product's Lifecycle</link>"
893 section.
894 </para>
895</section>
896
897<section id='git'>
898 <title>Git</title>
899
900 <para>
901 The Yocto Project makes extensive use of Git,
902 which is a free, open source distributed version control system.
903 Git supports distributed development, non-linear development, and can handle large projects.
904 It is best that you have some fundamental understanding of how Git tracks projects and
905 how to work with Git if you are going to use the Yocto Project for development.
906 This section provides a quick overview of how Git works and provides you with a summary
907 of some essential Git commands.
908 </para>
909
910 <para>
911 For more information on Git, see
912 <ulink url='http://git-scm.com/documentation'></ulink>.
913 If you need to download Git, go to <ulink url='http://git-scm.com/download'></ulink>.
914 </para>
915
916 <section id='repositories-tags-and-branches'>
917 <title>Repositories, Tags, and Branches</title>
918
919 <para>
920 As mentioned earlier in the section
921 "<link linkend='yocto-project-repositories'>Yocto Project Source Repositories</link>",
922 the Yocto Project maintains source repositories at
923 <ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink>.
924 If you look at this web-interface of the repositories, each item is a separate
925 Git repository.
926 </para>
927
928 <para>
929 Git repositories use branching techniques that track content change (not files)
930 within a project (e.g. a new feature or updated documentation).
931 Creating a tree-like structure based on project divergence allows for excellent historical
932 information over the life of a project.
933 This methodology also allows for an environment from which you can do lots of
934 local experimentation on projects as you develop changes or new features.
935 </para>
936
937 <para>
938 A Git repository represents all development efforts for a given project.
939 For example, the Git repository <filename>poky</filename> contains all changes
940 and developments for Poky over the course of its entire life.
941 That means that all changes that make up all releases are captured.
942 The repository maintains a complete history of changes.
943 </para>
944
945 <para>
946 You can create a local copy of any repository by "cloning" it with the Git
947 <filename>clone</filename> command.
948 When you clone a Git repository, you end up with an identical copy of the
949 repository on your development system.
950 Once you have a local copy of a repository, you can take steps to develop locally.
951 For examples on how to clone Git repositories, see the
952 "<link linkend='getting-setup'>Getting Set Up</link>" section.
953 </para>
954
955 <para>
956 It is important to understand that Git tracks content change and
957 not files.
958 Git uses "branches" to organize different development efforts.
959 For example, the <filename>poky</filename> repository has
960 <filename>denzil</filename>, <filename>danny</filename>,
961 <filename>dylan</filename>, <filename>dora</filename>,
962 <filename>daisy</filename>, and <filename>master</filename> branches
963 among others.
964 You can see all the branches by going to
965 <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/'></ulink> and
966 clicking on the
967 <filename><ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/refs/heads'>[...]</ulink></filename>
968 link beneath the "Branch" heading.
969 </para>
970
971 <para>
972 Each of these branches represents a specific area of development.
973 The <filename>master</filename> branch represents the current or most recent
974 development.
975 All other branches represent off-shoots of the <filename>master</filename>
976 branch.
977 </para>
978
979 <para>
980 When you create a local copy of a Git repository, the copy has the same set
981 of branches as the original.
982 This means you can use Git to create a local working area (also called a branch)
983 that tracks a specific development branch from the source Git repository.
984 in other words, you can define your local Git environment to work on any development
985 branch in the repository.
986 To help illustrate, here is a set of commands that creates a local copy of the
987 <filename>poky</filename> Git repository and then creates and checks out a local
988 Git branch that tracks the Yocto Project &DISTRO; Release (&DISTRO_NAME;) development:
989 <literallayout class='monospaced'>
990 $ cd ~
991 $ git clone git://git.yoctoproject.org/poky
992 $ cd poky
993 $ git checkout -b &DISTRO_NAME; origin/&DISTRO_NAME;
994 </literallayout>
995 In this example, the name of the top-level directory of your local
996 <link linkend='source-directory'>Source Directory</link>
997 is "poky" and the name of that local working area (local branch)
998 you just created and checked out is "&DISTRO_NAME;".
999 The files in your local repository now reflect the same files that
1000 are in the "&DISTRO_NAME;" development branch of the
1001 Yocto Project's "poky" upstream repository.
1002 It is important to understand that when you create and checkout a
1003 local working branch based on a branch name,
1004 your local environment matches the "tip" of that development branch
1005 at the time you created your local branch, which could be
1006 different from the files at the time of a similarly named release.
1007 In other words, creating and checking out a local branch based on
1008 the "&DISTRO_NAME;" branch name is not the same as
1009 cloning and checking out the "master" branch.
1010 Keep reading to see how you create a local snapshot of a Yocto
1011 Project Release.
1012 </para>
1013
1014 <para>
1015 Git uses "tags" to mark specific changes in a repository.
1016 Typically, a tag is used to mark a special point such as the final
1017 change before a project is released.
1018 You can see the tags used with the <filename>poky</filename> Git
1019 repository by going to
1020 <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/'></ulink> and
1021 clicking on the
1022 <filename><ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/refs/tags'>[...]</ulink></filename>
1023 link beneath the "Tag" heading.
1024 </para>
1025
1026 <para>
1027 Some key tags are <filename>dylan-9.0.0</filename>,
1028 <filename>dora-10.0.0</filename>,
1029 and <filename>&DISTRO_NAME;-&POKYVERSION;</filename>.
1030 These tags represent Yocto Project releases.
1031 </para>
1032
1033 <para>
1034 When you create a local copy of the Git repository, you also have access to all the
1035 tags.
1036 Similar to branches, you can create and checkout a local working Git branch based
1037 on a tag name.
1038 When you do this, you get a snapshot of the Git repository that reflects
1039 the state of the files when the change was made associated with that tag.
1040 The most common use is to checkout a working branch that matches a specific
1041 Yocto Project release.
1042 Here is an example:
1043 <literallayout class='monospaced'>
1044 $ cd ~
1045 $ git clone git://git.yoctoproject.org/poky
1046 $ cd poky
1047 $ git checkout -b my-&DISTRO_NAME;-&POKYVERSION; &DISTRO_NAME;-&POKYVERSION;
1048 </literallayout>
1049 In this example, the name of the top-level directory of your local Yocto Project
1050 Files Git repository is <filename>poky</filename>.
1051 And, the name of the local branch you have created and checked out is
1052 <filename>my-&DISTRO_NAME;-&POKYVERSION;</filename>.
1053 The files in your repository now exactly match the Yocto Project &DISTRO;
1054 Release tag (<filename>&DISTRO_NAME;-&POKYVERSION;</filename>).
1055 It is important to understand that when you create and checkout a local
1056 working branch based on a tag, your environment matches a specific point
1057 in time and not the entire development branch.
1058 </para>
1059 </section>
1060
1061 <section id='basic-commands'>
1062 <title>Basic Commands</title>
1063
1064 <para>
1065 Git has an extensive set of commands that lets you manage changes and perform
1066 collaboration over the life of a project.
1067 Conveniently though, you can manage with a small set of basic operations and workflows
1068 once you understand the basic philosophy behind Git.
1069 You do not have to be an expert in Git to be functional.
1070 A good place to look for instruction on a minimal set of Git commands is
1071 <ulink url='http://git-scm.com/documentation'>here</ulink>.
1072 If you need to download Git, you can do so
1073 <ulink url='http://git-scm.com/download'>here</ulink>.
1074 </para>
1075
1076 <para>
1077 If you do not know much about Git, you should educate
1078 yourself by visiting the links previously mentioned.
1079 </para>
1080
1081 <para>
1082 The following list briefly describes some basic Git operations as a way to get started.
1083 As with any set of commands, this list (in most cases) simply shows the base command and
1084 omits the many arguments they support.
1085 See the Git documentation for complete descriptions and strategies on how to use these commands:
1086 <itemizedlist>
1087 <listitem><para><emphasis><filename>git init</filename>:</emphasis> Initializes an empty Git repository.
1088 You cannot use Git commands unless you have a <filename>.git</filename> repository.</para></listitem>
1089 <listitem><para><emphasis><filename>git clone</filename>:</emphasis>
1090 Creates a local clone of a Git repository.
1091 During collaboration, this command allows you to create a
1092 local Git repository that is on equal footing with a fellow
1093 developer’s Git repository.
1094 </para></listitem>
1095 <listitem><para><emphasis><filename>git add</filename>:</emphasis> Stages updated file contents
1096 to the index that
1097 Git uses to track changes.
1098 You must stage all files that have changed before you can commit them.</para></listitem>
1099 <listitem><para><emphasis><filename>git commit</filename>:</emphasis> Creates a "commit" that documents
1100 the changes you made.
1101 Commits are used for historical purposes, for determining if a maintainer of a project
1102 will allow the change, and for ultimately pushing the change from your local Git repository
1103 into the project’s upstream (or master) repository.</para></listitem>
1104 <listitem><para><emphasis><filename>git status</filename>:</emphasis> Reports any modified files that
1105 possibly need to be staged and committed.</para></listitem>
1106 <listitem><para><emphasis><filename>git checkout &lt;branch-name&gt;</filename>:</emphasis> Changes
1107 your working branch.
1108 This command is analogous to "cd".</para></listitem>
1109 <listitem><para><emphasis><filename>git checkout –b &lt;working-branch&gt;</filename>:</emphasis> Creates
1110 a working branch on your local machine where you can isolate work.
1111 It is a good idea to use local branches when adding specific features or changes.
1112 This way if you do not like what you have done you can easily get rid of the work.</para></listitem>
1113 <listitem><para><emphasis><filename>git branch</filename>:</emphasis> Reports
1114 existing local branches and
1115 tells you the branch in which you are currently working.</para></listitem>
1116 <listitem><para><emphasis><filename>git branch -D &lt;branch-name&gt;</filename>:</emphasis>
1117 Deletes an existing local branch.
1118 You need to be in a local branch other than the one you are deleting
1119 in order to delete <filename>&lt;branch-name&gt;</filename>.</para></listitem>
1120 <listitem><para><emphasis><filename>git pull</filename>:</emphasis> Retrieves information
1121 from an upstream Git
1122 repository and places it in your local Git repository.
1123 You use this command to make sure you are synchronized with the repository
1124 from which you are basing changes (.e.g. the master branch).</para></listitem>
1125 <listitem><para><emphasis><filename>git push</filename>:</emphasis>
1126 Sends all your committed local changes to an upstream Git
1127 repository (e.g. a contribution repository).
1128 The maintainer of the project draws from these repositories
1129 when adding changes to the project’s master repository or
1130 other development branch.
1131 </para></listitem>
1132 <listitem><para><emphasis><filename>git merge</filename>:</emphasis> Combines or adds changes from one
1133 local branch of your repository with another branch.
1134 When you create a local Git repository, the default branch is named "master".
1135 A typical workflow is to create a temporary branch for isolated work, make and commit your
1136 changes, switch to your local master branch, merge the changes from the temporary branch into the
1137 local master branch, and then delete the temporary branch.</para></listitem>
1138 <listitem><para><emphasis><filename>git cherry-pick</filename>:</emphasis> Choose and apply specific
1139 commits from one branch into another branch.
1140 There are times when you might not be able to merge all the changes in one branch with
1141 another but need to pick out certain ones.</para></listitem>
1142 <listitem><para><emphasis><filename>gitk</filename>:</emphasis> Provides a GUI view of the branches
1143 and changes in your local Git repository.
1144 This command is a good way to graphically see where things have diverged in your
1145 local repository.</para></listitem>
1146 <listitem><para><emphasis><filename>git log</filename>:</emphasis> Reports a history of your changes to the
1147 repository.</para></listitem>
1148 <listitem><para><emphasis><filename>git diff</filename>:</emphasis> Displays line-by-line differences
1149 between your local working files and the same files in the upstream Git repository that your
1150 branch currently tracks.</para></listitem>
1151 </itemizedlist>
1152 </para>
1153 </section>
1154</section>
1155
1156<section id='workflows'>
1157 <title>Workflows</title>
1158
1159 <para>
1160 This section provides some overview on workflows using Git.
1161 In particular, the information covers basic practices that describe roles and actions in a
1162 collaborative development environment.
1163 Again, if you are familiar with this type of development environment, you might want to just
1164 skip this section.
1165 </para>
1166
1167 <para>
1168 The Yocto Project files are maintained using Git in a "master" branch whose Git history
1169 tracks every change and whose structure provides branches for all diverging functionality.
1170 Although there is no need to use Git, many open source projects do so.
1171 For the Yocto Project, a key individual called the "maintainer" is responsible for the "master"
1172 branch of a given Git repository.
1173 The "master" branch is the “upstream” repository where the final builds of the project occur.
1174 The maintainer is responsible for allowing changes in from other developers and for
1175 organizing the underlying branch structure to reflect release strategies and so forth.
1176 <note>For information on finding out who is responsible (maintains)
1177 for a particular area of code, see the
1178 "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
1179 section.
1180 </note>
1181 </para>
1182
1183 <para>
1184 The project also has an upstream contribution Git repository named
1185 <filename>poky-contrib</filename>.
1186 You can see all the branches in this repository using the web interface
1187 of the
1188 <ulink url='&YOCTO_GIT_URL;'>Source Repositories</ulink> organized
1189 within the "Poky Support" area.
1190 These branches temporarily hold changes to the project that have been
1191 submitted or committed by the Yocto Project development team and by
1192 community members who contribute to the project.
1193 The maintainer determines if the changes are qualified to be moved
1194 from the "contrib" branches into the "master" branch of the Git
1195 repository.
1196 </para>
1197
1198 <para>
1199 Developers (including contributing community members) create and maintain cloned repositories
1200 of the upstream "master" branch.
1201 These repositories are local to their development platforms and are used to develop changes.
1202 When a developer is satisfied with a particular feature or change, they "push" the changes
1203 to the appropriate "contrib" repository.
1204 </para>
1205
1206 <para>
1207 Developers are responsible for keeping their local repository up-to-date with "master".
1208 They are also responsible for straightening out any conflicts that might arise within files
1209 that are being worked on simultaneously by more than one person.
1210 All this work is done locally on the developer’s machines before anything is pushed to a
1211 "contrib" area and examined at the maintainer’s level.
1212 </para>
1213
1214 <para>
1215 A somewhat formal method exists by which developers commit changes and push them into the
1216 "contrib" area and subsequently request that the maintainer include them into "master"
1217 This process is called “submitting a patch” or "submitting a change."
1218 For information on submitting patches and changes, see the
1219 "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>" section.
1220 </para>
1221
1222 <para>
1223 To summarize the environment: a single point of entry exists for
1224 changes into the project’s "master" branch of the Git repository,
1225 which is controlled by the project’s maintainer.
1226 And, a set of developers exist who independently develop, test, and
1227 submit changes to "contrib" areas for the maintainer to examine.
1228 The maintainer then chooses which changes are going to become a
1229 permanent part of the project.
1230 </para>
1231
1232 <para>
1233 <imagedata fileref="figures/git-workflow.png" width="6in" depth="3in" align="left" scalefit="1" />
1234 </para>
1235
1236 <para>
1237 While each development environment is unique, there are some best practices or methods
1238 that help development run smoothly.
1239 The following list describes some of these practices.
1240 For more information about Git workflows, see the workflow topics in the
1241 <ulink url='http://book.git-scm.com'>Git Community Book</ulink>.
1242 <itemizedlist>
1243 <listitem><para><emphasis>Make Small Changes:</emphasis> It is best to keep the changes you commit
1244 small as compared to bundling many disparate changes into a single commit.
1245 This practice not only keeps things manageable but also allows the maintainer
1246 to more easily include or refuse changes.</para>
1247 <para>It is also good practice to leave the repository in a state that allows you to
1248 still successfully build your project. In other words, do not commit half of a feature,
1249 then add the other half as a separate, later commit.
1250 Each commit should take you from one buildable project state to another
1251 buildable state.</para></listitem>
1252 <listitem><para><emphasis>Use Branches Liberally:</emphasis> It is very easy to create, use, and
1253 delete local branches in your working Git repository.
1254 You can name these branches anything you like.
1255 It is helpful to give them names associated with the particular feature or change
1256 on which you are working.
1257 Once you are done with a feature or change and have merged it
1258 into your local master branch, simply discard the temporary
1259 branch.</para></listitem>
1260 <listitem><para><emphasis>Merge Changes:</emphasis> The <filename>git merge</filename>
1261 command allows you to take the
1262 changes from one branch and fold them into another branch.
1263 This process is especially helpful when more than a single developer might be working
1264 on different parts of the same feature.
1265 Merging changes also automatically identifies any collisions or "conflicts"
1266 that might happen as a result of the same lines of code being altered by two different
1267 developers.</para></listitem>
1268 <listitem><para><emphasis>Manage Branches:</emphasis> Because branches are easy to use, you should
1269 use a system where branches indicate varying levels of code readiness.
1270 For example, you can have a "work" branch to develop in, a "test" branch where the code or
1271 change is tested, a "stage" branch where changes are ready to be committed, and so forth.
1272 As your project develops, you can merge code across the branches to reflect ever-increasing
1273 stable states of the development.</para></listitem>
1274 <listitem><para><emphasis>Use Push and Pull:</emphasis> The push-pull workflow is based on the
1275 concept of developers "pushing" local commits to a remote repository, which is
1276 usually a contribution repository.
1277 This workflow is also based on developers "pulling" known states of the project down into their
1278 local development repositories.
1279 The workflow easily allows you to pull changes submitted by other developers from the
1280 upstream repository into your work area ensuring that you have the most recent software
1281 on which to develop.
1282 The Yocto Project has two scripts named <filename>create-pull-request</filename> and
1283 <filename>send-pull-request</filename> that ship with the release to facilitate this
1284 workflow.
1285 You can find these scripts in the <filename>scripts</filename>
1286 folder of the
1287 <link linkend='source-directory'>Source Directory</link>.
1288 For information on how to use these scripts, see the
1289 "<link linkend='pushing-a-change-upstream'>Using Scripts to Push a Change Upstream and Request a Pull</link>" section.
1290 </para></listitem>
1291 <listitem><para><emphasis>Patch Workflow:</emphasis> This workflow allows you to notify the
1292 maintainer through an email that you have a change (or patch) you would like considered
1293 for the "master" branch of the Git repository.
1294 To send this type of change, you format the patch and then send the email using the Git commands
1295 <filename>git format-patch</filename> and <filename>git send-email</filename>.
1296 For information on how to use these scripts, see the
1297 "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
1298 section.
1299 </para></listitem>
1300 </itemizedlist>
1301 </para>
1302</section>
1303
1304<section id='tracking-bugs'>
1305 <title>Tracking Bugs</title>
1306
1307 <para>
1308 The Yocto Project uses its own implementation of
1309 <ulink url='http://www.bugzilla.org/about/'>Bugzilla</ulink> to track bugs.
1310 Implementations of Bugzilla work well for group development because they track bugs and code
1311 changes, can be used to communicate changes and problems with developers, can be used to
1312 submit and review patches, and can be used to manage quality assurance.
1313 The home page for the Yocto Project implementation of Bugzilla is
1314 <ulink url='&YOCTO_BUGZILLA_URL;'>&YOCTO_BUGZILLA_URL;</ulink>.
1315 </para>
1316
1317 <para>
1318 Sometimes it is helpful to submit, investigate, or track a bug against the Yocto Project itself
1319 such as when discovering an issue with some component of the build system that acts contrary
1320 to the documentation or your expectations.
1321 Following is the general procedure for submitting a new bug using the Yocto Project
1322 Bugzilla.
1323 You can find more information on defect management, bug tracking, and feature request
1324 processes all accomplished through the Yocto Project Bugzilla on the wiki page
1325 <ulink url='&YOCTO_WIKI_URL;/wiki/Bugzilla_Configuration_and_Bug_Tracking'>here</ulink>.
1326 <orderedlist>
1327 <listitem><para>Always use the Yocto Project implementation of Bugzilla to submit
1328 a bug.</para></listitem>
1329 <listitem><para>When submitting a new bug, be sure to choose the appropriate
1330 Classification, Product, and Component for which the issue was found.
1331 Defects for the Yocto Project fall into one of six classifications: Yocto Project
1332 Components, Infrastructure, Build System &amp; Metadata, Documentation,
1333 QA/Testing, and Runtime.
1334 Each of these Classifications break down into multiple Products and, in some
1335 cases, multiple Components.</para></listitem>
1336 <listitem><para>Use the bug form to choose the correct Hardware and Architecture
1337 for which the bug applies.</para></listitem>
1338 <listitem><para>Indicate the Yocto Project version you were using when the issue
1339 occurred.</para></listitem>
1340 <listitem><para>Be sure to indicate the Severity of the bug.
1341 Severity communicates how the bug impacted your work.</para></listitem>
1342 <listitem><para>Select the appropriate "Documentation change" item
1343 for the bug.
1344 Fixing a bug may or may not affect the Yocto Project
1345 documentation.</para></listitem>
1346 <listitem><para>Provide a brief summary of the issue.
1347 Try to limit your summary to just a line or two and be sure to capture the
1348 essence of the issue.</para></listitem>
1349 <listitem><para>Provide a detailed description of the issue.
1350 You should provide as much detail as you can about the context, behavior, output,
1351 and so forth that surrounds the issue.
1352 You can even attach supporting files for output from logs by
1353 using the "Add an attachment" button.</para></listitem>
1354 <listitem><para>Be sure to copy the appropriate people in the
1355 "CC List" for the bug.
1356 See the "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
1357 section for information about finding out who is responsible
1358 for code.</para></listitem>
1359 <listitem><para>Submit the bug by clicking the "Submit Bug" button.</para></listitem>
1360 </orderedlist>
1361 </para>
1362</section>
1363
1364<section id='how-to-submit-a-change'>
1365 <title>How to Submit a Change</title>
1366
1367 <para>
1368 Contributions to the Yocto Project and OpenEmbedded are very welcome.
1369 Because the system is extremely configurable and flexible, we recognize that developers
1370 will want to extend, configure or optimize it for their specific uses.
1371 You should send patches to the appropriate mailing list so that they
1372 can be reviewed and merged by the appropriate maintainer.
1373 </para>
1374
1375 <para>
1376 Before submitting any change, be sure to find out who you should be
1377 notifying.
1378 Several methods exist through which you find out who you should be copying
1379 or notifying:
1380 <itemizedlist>
1381 <listitem><para><emphasis>Maintenance File:</emphasis>
1382 Examine the <filename>maintainers.inc</filename> file, which is
1383 located in the
1384 <link linkend='source-directory'>Source Directory</link>
1385 at <filename>meta-yocto/conf/distro/include</filename>, to
1386 see who is responsible for code.
1387 </para></listitem>
1388 <listitem><para><emphasis>Board Support Package (BSP) README Files:</emphasis>
1389 For BSP maintainers of supported BSPs, you can examine
1390 individual BSP <filename>README</filename> files.
1391 In addition, some layers (such as the <filename>meta-intel</filename> layer),
1392 include a <filename>MAINTAINERS</filename> file which contains
1393 a list of all supported BSP maintainers for that layer.
1394 </para></listitem>
1395 <listitem><para><emphasis>Search by File:</emphasis>
1396 Using <link linkend='git'>Git</link>, you can enter the
1397 following command to bring up a short list of all commits
1398 against a specific file:
1399 <literallayout class='monospaced'>
1400 git shortlog -- &lt;filename&gt;
1401 </literallayout>
1402 Just provide the name of the file for which you are interested.
1403 The information returned is not ordered by history but does
1404 include a list of all committers grouped by name.
1405 From the list, you can see who is responsible for the bulk of
1406 the changes against the file.
1407 </para></listitem>
1408 </itemizedlist>
1409 </para>
1410
1411 <para>
1412 For a list of the Yocto Project and related mailing lists, see the
1413 "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing lists</ulink>" section in
1414 the Yocto Project Reference Manual.
1415 </para>
1416
1417 <para>
1418 Here is some guidance on which mailing list to use for what type of change:
1419 <itemizedlist>
1420 <listitem><para>For changes to the core
1421 <link linkend='metadata'>Metadata</link>, send your patch to the
1422 <ulink url='&OE_LISTS_URL;/listinfo/openembedded-core'>openembedded-core</ulink> mailing list.
1423 For example, a change to anything under the <filename>meta</filename> or
1424 <filename>scripts</filename> directories
1425 should be sent to this mailing list.</para></listitem>
1426 <listitem><para>For changes to BitBake (anything under the <filename>bitbake</filename>
1427 directory), send your patch to the
1428 <ulink url='&OE_LISTS_URL;/listinfo/bitbake-devel'>bitbake-devel</ulink> mailing list.</para></listitem>
1429 <listitem><para>For changes to <filename>meta-yocto</filename>, send your patch to the
1430 <ulink url='&YOCTO_LISTS_URL;/listinfo/poky'>poky</ulink> mailing list.</para></listitem>
1431 <listitem><para>For changes to other layers hosted on
1432 <filename>yoctoproject.org</filename> (unless the
1433 layer's documentation specifies otherwise), tools, and Yocto Project
1434 documentation, use the
1435 <ulink url='&YOCTO_LISTS_URL;/listinfo/yocto'>yocto</ulink> mailing list.</para></listitem>
1436 <listitem><para>For additional recipes that do not fit into the core Metadata,
1437 you should determine which layer the recipe should go into and submit the
1438 change in the manner recommended by the documentation (e.g. README) supplied
1439 with the layer. If in doubt, please ask on the
1440 <ulink url='&YOCTO_LISTS_URL;/listinfo/yocto'>yocto</ulink> or
1441 <ulink url='&OE_LISTS_URL;/listinfo/openembedded-devel'>openembedded-devel</ulink>
1442 mailing lists.</para></listitem>
1443 </itemizedlist>
1444 </para>
1445
1446 <para>
1447 When you send a patch, be sure to include a "Signed-off-by:"
1448 line in the same style as required by the Linux kernel.
1449 Adding this line signifies that you, the submitter, have agreed to the Developer's Certificate of Origin 1.1
1450 as follows:
1451 <literallayout class='monospaced'>
1452 Developer's Certificate of Origin 1.1
1453
1454 By making a contribution to this project, I certify that:
1455
1456 (a) The contribution was created in whole or in part by me and I
1457 have the right to submit it under the open source license
1458 indicated in the file; or
1459
1460 (b) The contribution is based upon previous work that, to the best
1461 of my knowledge, is covered under an appropriate open source
1462 license and I have the right under that license to submit that
1463 work with modifications, whether created in whole or in part
1464 by me, under the same open source license (unless I am
1465 permitted to submit under a different license), as indicated
1466 in the file; or
1467
1468 (c) The contribution was provided directly to me by some other
1469 person who certified (a), (b) or (c) and I have not modified
1470 it.
1471
1472 (d) I understand and agree that this project and the contribution
1473 are public and that a record of the contribution (including all
1474 personal information I submit with it, including my sign-off) is
1475 maintained indefinitely and may be redistributed consistent with
1476 this project or the open source license(s) involved.
1477 </literallayout>
1478 </para>
1479
1480 <para>
1481 In a collaborative environment, it is necessary to have some sort of standard
1482 or method through which you submit changes.
1483 Otherwise, things could get quite chaotic.
1484 One general practice to follow is to make small, controlled changes.
1485 Keeping changes small and isolated aids review, makes merging/rebasing easier
1486 and keeps the change history clean when anyone needs to refer to it in future.
1487 </para>
1488
1489 <para>
1490 When you make a commit, you must follow certain standards established by the
1491 OpenEmbedded and Yocto Project development teams.
1492 For each commit, you must provide a single-line summary of the change and you
1493 should almost always provide a more detailed description of what you did (i.e.
1494 the body of the commit message).
1495 The only exceptions for not providing a detailed description would be if your
1496 change is a simple, self-explanatory change that needs no further description
1497 beyond the summary.
1498 Here are the guidelines for composing a commit message:
1499 <itemizedlist>
1500 <listitem><para>Provide a single-line, short summary of the change.
1501 This summary is typically viewable in the "shortlist" of changes.
1502 Thus, providing something short and descriptive that gives the reader
1503 a summary of the change is useful when viewing a list of many commits.
1504 This short description should be prefixed by the recipe name (if changing a recipe), or
1505 else the short form path to the file being changed.
1506 </para></listitem>
1507 <listitem><para>For the body of the commit message, provide detailed information
1508 that describes what you changed, why you made the change, and the approach
1509 you used. It may also be helpful if you mention how you tested the change.
1510 Provide as much detail as you can in the body of the commit message.
1511 </para></listitem>
1512 <listitem><para>
1513 If the change addresses a specific bug or issue that is
1514 associated with a bug-tracking ID, include a reference to that
1515 ID in your detailed description.
1516 For example, the Yocto Project uses a specific convention for
1517 bug references - any commit that addresses a specific bug should
1518 use the following form for the detailed description:
1519 <literallayout class='monospaced'>
1520 Fixes [YOCTO #&lt;bug-id&gt;]
1521
1522 &lt;detailed description of change&gt;
1523 </literallayout></para></listitem>
1524 Where &lt;bug-id&gt; is replaced with the specific bug ID from
1525 the Yocto Project Bugzilla instance.
1526 </itemizedlist>
1527 </para>
1528
1529 <para>
1530 You can find more guidance on creating well-formed commit messages at this OpenEmbedded
1531 wiki page:
1532 <ulink url='&OE_HOME_URL;/wiki/Commit_Patch_Message_Guidelines'></ulink>.
1533 </para>
1534
1535 <para>
1536 The next two sections describe general instructions for both pushing
1537 changes upstream and for submitting changes as patches.
1538 </para>
1539
1540 <section id='pushing-a-change-upstream'>
1541 <title>Using Scripts to Push a Change Upstream and Request a Pull</title>
1542
1543 <para>
1544 The basic flow for pushing a change to an upstream "contrib" Git repository is as follows:
1545 <itemizedlist>
1546 <listitem><para>Make your changes in your local Git repository.</para></listitem>
1547 <listitem><para>Stage your changes by using the <filename>git add</filename>
1548 command on each file you changed.</para></listitem>
1549 <listitem><para>
1550 Commit the change by using the
1551 <filename>git commit</filename> command.
1552 Be sure to provide a commit message that follows the
1553 project’s commit message standards as described earlier.
1554 </para></listitem>
1555 <listitem><para>
1556 Push the change to the upstream "contrib" repository by
1557 using the <filename>git push</filename> command.
1558 </para></listitem>
1559 <listitem><para>Notify the maintainer that you have pushed a change by making a pull
1560 request.
1561 The Yocto Project provides two scripts that conveniently let you generate and send
1562 pull requests to the Yocto Project.
1563 These scripts are <filename>create-pull-request</filename> and
1564 <filename>send-pull-request</filename>.
1565 You can find these scripts in the <filename>scripts</filename> directory
1566 within the <link linkend='source-directory'>Source Directory</link>.</para>
1567 <para>Using these scripts correctly formats the requests without introducing any
1568 whitespace or HTML formatting.
1569 The maintainer that receives your patches needs to be able to save and apply them
1570 directly from your emails.
1571 Using these scripts is the preferred method for sending patches.</para>
1572 <para>For help on using these scripts, simply provide the
1573 <filename>-h</filename> argument as follows:
1574 <literallayout class='monospaced'>
1575 $ poky/scripts/create-pull-request -h
1576 $ poky/scripts/send-pull-request -h
1577 </literallayout></para></listitem>
1578 </itemizedlist>
1579 </para>
1580
1581 <para>
1582 You can find general Git information on how to push a change upstream in the
1583 <ulink url='http://book.git-scm.com/3_distributed_workflows.html'>Git Community Book</ulink>.
1584 </para>
1585 </section>
1586
1587 <section id='submitting-a-patch'>
1588 <title>Using Email to Submit a Patch</title>
1589
1590 <para>
1591 You can submit patches without using the <filename>create-pull-request</filename> and
1592 <filename>send-pull-request</filename> scripts described in the previous section.
1593 However, keep in mind, the preferred method is to use the scripts.
1594 </para>
1595
1596 <para>
1597 Depending on the components changed, you need to submit the email to a specific
1598 mailing list.
1599 For some guidance on which mailing list to use, see the list in the
1600 "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
1601 section.
1602 For a description of the available mailing lists, see the
1603 "<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Mailing Lists</ulink>"
1604 section in the Yocto Project Reference Manual.
1605 </para>
1606
1607 <para>
1608 Here is the general procedure on how to submit a patch through email without using the
1609 scripts:
1610 <itemizedlist>
1611 <listitem><para>Make your changes in your local Git repository.</para></listitem>
1612 <listitem><para>Stage your changes by using the <filename>git add</filename>
1613 command on each file you changed.</para></listitem>
1614 <listitem><para>Commit the change by using the
1615 <filename>git commit --signoff</filename> command.
1616 Using the <filename>--signoff</filename> option identifies you as the person
1617 making the change and also satisfies the Developer's Certificate of
1618 Origin (DCO) shown earlier.</para>
1619 <para>When you form a commit, you must follow certain standards established by the
1620 Yocto Project development team.
1621 See the earlier section
1622 "<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
1623 for Yocto Project commit message standards.</para></listitem>
1624 <listitem><para>Format the commit into an email message.
1625 To format commits, use the <filename>git format-patch</filename> command.
1626 When you provide the command, you must include a revision list or a number of patches
1627 as part of the command.
1628 For example, either of these two commands takes your most
1629 recent single commit and formats it as an email message in
1630 the current directory:
1631 <literallayout class='monospaced'>
1632 $ git format-patch -1
1633 </literallayout>
1634 or
1635 <literallayout class='monospaced'>
1636 $ git format-patch HEAD~
1637 </literallayout></para>
1638 <para>After the command is run, the current directory contains a
1639 numbered <filename>.patch</filename> file for the commit.</para>
1640 <para>If you provide several commits as part of the command,
1641 the <filename>git format-patch</filename> command produces a
1642 series of numbered files in the current directory – one for each commit.
1643 If you have more than one patch, you should also use the
1644 <filename>--cover</filename> option with the command, which generates a
1645 cover letter as the first "patch" in the series.
1646 You can then edit the cover letter to provide a description for
1647 the series of patches.
1648 For information on the <filename>git format-patch</filename> command,
1649 see <filename>GIT_FORMAT_PATCH(1)</filename> displayed using the
1650 <filename>man git-format-patch</filename> command.</para>
1651 <note>If you are or will be a frequent contributor to the Yocto Project
1652 or to OpenEmbedded, you might consider requesting a contrib area and the
1653 necessary associated rights.</note></listitem>
1654 <listitem><para>Import the files into your mail client by using the
1655 <filename>git send-email</filename> command.
1656 <note>In order to use <filename>git send-email</filename>, you must have the
1657 the proper Git packages installed.
1658 For Ubuntu, Debian, and Fedora the package is <filename>git-email</filename>.</note></para>
1659 <para>The <filename>git send-email</filename> command sends email by using a local
1660 or remote Mail Transport Agent (MTA) such as
1661 <filename>msmtp</filename>, <filename>sendmail</filename>, or through a direct
1662 <filename>smtp</filename> configuration in your Git <filename>config</filename>
1663 file.
1664 If you are submitting patches through email only, it is very important
1665 that you submit them without any whitespace or HTML formatting that
1666 either you or your mailer introduces.
1667 The maintainer that receives your patches needs to be able to save and
1668 apply them directly from your emails.
1669 A good way to verify that what you are sending will be applicable by the
1670 maintainer is to do a dry run and send them to yourself and then
1671 save and apply them as the maintainer would.</para>
1672 <para>The <filename>git send-email</filename> command is the preferred method
1673 for sending your patches since there is no risk of compromising whitespace
1674 in the body of the message, which can occur when you use your own mail client.
1675 The command also has several options that let you
1676 specify recipients and perform further editing of the email message.
1677 For information on how to use the <filename>git send-email</filename> command,
1678 see <filename>GIT-SEND-EMAIL(1)</filename> displayed using
1679 the <filename>man git-send-email</filename> command.
1680 </para></listitem>
1681 </itemizedlist>
1682 </para>
1683 </section>
1684</section>
1685</chapter>
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